Streaming media formats: RealMedia and RealAudio
RealMedia is the most widely adopted streaming media format on the Web. Its popularity is due in large part to the fact that it was the first streaming technology on the market. But it's popular also because of RealNetworks' laser focus on ease of use, deployment of a wide palette of developer tools, continuous support for the latest multimedia technologies, and support for both Windows and Unix platforms. RealMedia is the format of choice for professionals who want advanced controls for serving, tracking, and managing large numbers of audio streams. RealNetworks has been a trailblazer in making advanced server features, which were once accessible only to those with advanced programming skills, available to the public.
And RealMedia is likely to attract more fans as web developers begin to use the RealSystem G2 and SMIL to stream synchronized multimedia presentations over the Web. G2's major advance is the ability to simultaneously stream multiple media types as separate files instead of as one RealMedia-encoded file. This makes updating multimedia content easier, since you can simply upload one element of a presentation instead of re-encoding the whole media file.
Perhaps the most powerful feature of RealSystem G2 is RealNetworks' server architecture. Broadcasting audio with a dedicated RealServer provides the following advantages over HTTP pseudo-streaming from a standard web server:
- Bandwidth negotiation
- Ensures that all users receive the
appropriate encoded content for the best audio quality at their available
bandwidth, from slower analog modems to faster cable or xDSL connections.
RealSystem G2's new SureStream technology is even more efficient than
bandwidth negotiation. SureStream can dynamically change data rates midstream
to accommodate fluctuating bandwidth.
- Robust RTSP transmission
- Detects and compensates for lost
packets, maintaining smooth, continuous audio playback--something that HTTP
streaming can't deliver.
- Splitting
- Allows for splitting and routing
the audio signal from one RealServer to other RealServers located at different
points across the Internet.
- Clustering
- Allows multiple RealServers to be
clustered together so they work as a single, multiprocessor machine.
- IP multicasting
- Allows all users of a network to
listen to a single live stream, making efficient use of network resources.
Multicasting avoids delivering numerous simultaneous point-to-point
connections by broadcasting one stream to a certain point in the network where
other users are requesting the same file. Multicasting is ideal for reducing
server load and bandwidth congestion during live broadcasts.
While RealMedia's powerful server-side architecture supports and manages robust streaming to large audiences, this core strength results in limited interactivity. Like Windows Media and other server-side streaming technologies, RealMedia waits for a request from a listener's browser before it begins to stream media files. This helps RealMedia negotiate bandwidth congestion on the fly by sending an appropriate size stream that matches the listener's real bandwidth. But it also produces a significant time gap of a few seconds between the listener's request and the response from the server. This small time gap is inconsequential with long-playing video and audio files, but it prohibits the use of interactive sound effects such as button rollovers, sound transitions from one page to another, and loops that must respond instantaneously to a mouse click.
Thus, RealMedia is inappropriate for high impact presentations with interactive sound effects and loops. Despite significant advancements in RealSystem G2, RealAudio still trails Flash and Director Shockwave when it comes to smooth playback of high-impact interactive multimedia. High-powered interactive media requires a client-side solution such as Flash, Shockwave, or Beatnik.
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